This invention relates generally to support mechanisms for stoppers used in casting measured quantities of molten steel and is particularly concerned with the provision of an improved mechanism enabling accurate location of the nose of the stopper relative to the well of the nozzle of the associated casting container.
It is established practice to control the feed of molten steel from a container to a mold by means of an elongate stopper located vertically within the container and having a lower nose end co-operating with a nozzle in the base of the container whereby axial movement of the stopper relative to the container opens and closes the nozzle in accordance with the desired rate of flow of the molten steel.
In one known arrangement, the upper end of the stopper is rigidly connected to one end of a transverse connecting arm by means of a cylindrical rod. More particularly the lower extent of the rod is housed within the upper extent of the stopper to extend axially of the stopper, a pin extending diametrically through the stopper and the cylindrical rod to secure the stopper to the rod, while the upper, threaded extent of the rod extends through a slot in the one end of the transverse rod and is secured to said rod by a series of washers, nuts and lock-nuts both above and below said rod.
The other end of the transverse connecting arm is mounted to the upper end of a vertical shaft located outside the container, said upper end of the shaft being threaded and projecting through a receiving hole in the other end of the connecting arm to which it is connected by means of a series of washers, nuts and lock-nuts.
Integrally formed in the lower regions of the vertical shaft is a rack with which co-operates a rotatable pinion in such a manner that rotation of the pinion results in axially upward or downward movement of the shaft and attached components.
Thus it will be appreciated that there has been described a substantially inverted U-shaped support mechanism for the stopper which can be moved bodily upwards and downwards relative to the container to adjust the axial position of the nose end of the stopper relative to the nozzle and by which the stopper can be pivoted about the central vertical axis of the shaft to provide arcuate adjustment in a horizontal plane of the position of the nose end of the stopper relative to the nozzle.
Such arrangements suffer from a number of disadvantages. Not the least of these is that, although the axial position of the nose end of the stopper can be accurately determined, the precise location of the stopper nose end in a horizontal plane cannot, because the stopper can only be swung about a fixed vertical axis. For controlled casting it is essential for the central longitudinal axis of the stopper to be co-axial with, and form a continuation of, the central axis of the nozzle. Existing arrangements cannot ensure such a situation.
Further, the provision of a diametrical pin and the drilling of the stopper to receive the pin to enable the stopper to be secured to the one end of the connecting arm is a distinct mechanical weak-spot in the support mechanism and is extremely prone to breakage--once this part of the stopper breaks, the stopper becomes unsupported.
The stopper includes a central bore through which an inert gas such as argon can be fed to the nose end thereof during casting. Said gas, which amongst other things attempts to reduce the build-up of alumina and cold steel at the nozzle, is fed to the bore in the stopper by means of a radial passage provided in one of the above-mentioned washers incorporated in the means connecting the cylindrical rod to the transverse arm and to which washer is connected a supply of said gas. The nature of said connection means is such that the path of the gas from the supply to the bore in the stopper is very prone to leakage whereby substantial volumes of gas can be lost to atmosphere.
Substantial build-up of undesirable deposits in the nozzle can occur in the known arrangement despite the presence of the argon gas, and clearance is usually achieved by raising the container to disengage the nozzle from the mould, inserting a lance up the nozzle and feeding oxygen to the well of the nozzle through said lance. However this can often cause irrepairable damage to the nozzle with the result that the cast has to be aborted.
If oxygen were to be fed to the nozzle by way of the central bore in the stopper,--i.e. the argon feed path--the intense heat created would be such as to melt the pin securing the stopper to the cylindrical rod, thus causing the stopper to break away from its support mechanism.
It would be desirable to be able to provide a stopper support mechanism less prone to the above disadvantages and in particular mechanically stronger and more maneuverable than the known arrangement.